Optical encryption steganography method and system based on multi-channel metasurface

Abstract

The present invention proposes a multi-channel metasurface-based optical encryption steganography method and system, relating to the field of metasurface optical encryption technology. The method mainly comprises: constructing a dual-structured non-spatial-multiplexed three-channel metasurface based on the material properties of a dual-wavelength metasurface; encoding a first meta-image used to transmit secret information extraction and recovery parameters, as well as a second meta-image and a third meta-image embedded with secret information using a run-length encoding-based steganography algorithm, into the dual-structured non-spatial-multiplexed three-channel metasurface for optical encryption, and decrypting them requires optical keys of different levels. The present invention can reduce the risk of information being easily cracked by exhaustive analysis due to a single key level, and utilizes a multi-carrier information steganography method to prevent direct observation of optically encrypted information.

Description

Technical Field

[0001] The present invention belongs to the field of metasurface optical encryption technology, and in particular relates to an optical encryption steganography method and system based on a multi-channel metasurface. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Information security is crucial in every aspect of life. To prevent information theft and tampering, various encryption technologies have emerged. Optical encryption, among other technologies, utilizes light interference, diffraction, and imaging to transform plaintext information into complex and difficult-to-interpret optical signals, providing an efficient and reliable solution for encrypting and processing highly secure information.

[0004] Metasurfaces are artificially designed two-dimensional planar optical metamaterials, typically composed of nanostructures, or metaatomic arrays, with customized shapes and subwavelength features. Due to their unprecedented ability to manipulate localized light fields at the subwavelength scale, metasurfaces have been successfully applied to a wide variety of compact and miniaturized planar functional devices, such as holographic displays, polarization conversion, light focusing, and vortex beams. Currently, metasurfaces are widely used to explore novel optical encryption by manipulating various photon degrees of freedom, such as polarization, amplitude, phase, and orbital angular momentum. In particular, the emergence of various multiplexed metasurfaces has made it possible to encode ultra-high-resolution multi-channel image information within the same metasurface. The image information in each channel requires specific optical illumination conditions, known as an optical key, to be observed, thus translating it into optical encryption of the multi-channel image information.

[0005] However, most current multi-channel optical encryption metasurfaces have a single optical key level. If the key of one channel is known, the keys of other channels can be easily cracked due to the same form, which seriously threatens the security of information. In addition, most of the currently proposed optical encryption metasurfaces encrypt plaintext information in the form of image display. The encrypted information is encoded in the form of image display in each channel of the metasurface, making the secret information directly observable, resulting in the risk of information being easily stolen. The existing advanced information encryption method that combines metasurfaces with cryptographic encryption algorithms has certain disadvantages. The presence of pseudo-random ciphertext information in multiple channels may arouse the suspicion of eavesdroppers, making the information vulnerable to censorship and cracking attempts. Summary of the Invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides an optical encryption steganography method and system based on a multi-channel metasurface, which can enable the multi-channel metasurface optical keys to have two levels, high and low, effectively reducing the risk of information being easily cracked by exhaustive means due to the single key level; and integrating multi-carrier information steganography into the field of metasurface optical encryption, effectively preventing optically encrypted information from being directly observed.

[0007] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0008] The first aspect of the present invention provides an optical encryption steganography method based on a multi-channel metasurface.

[0009] An optical encryption steganography method based on a multi-channel metasurface, comprising:

[0010] Based on the material properties of the dual-wavelength metasurface, a dual-structure non-spatial multiplexing three-channel metasurface is constructed;

[0011] Obtain secret information, perform scrambling preprocessing to obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first meta-image;

[0012] A steganographic algorithm based on run-length coding selects two carrier images. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images. The images are then reconstructed to obtain the second and third super-images embedded with the secret information.

[0013] The first meta-image, the second meta-image and the third meta-image are respectively encoded into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

[0014] A second aspect of the present invention provides an optical encryption steganography system based on a multi-channel metasurface.

[0015] An optical encryption steganography system based on a multi-channel metasurface, comprising:

[0016] The channel construction module is configured to: construct a dual-structure non-spatial multiplexing three-channel metasurface based on the material properties of the dual-wavelength metasurface;

[0017] The meta-image acquisition module is configured to: acquire secret information, perform scrambling preprocessing to obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first meta-image;

[0018] A steganographic algorithm based on run-length coding selects two carrier images. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images. The images are then reconstructed to obtain the second and third super-images embedded with the secret information.

[0019] The optical encryption module is configured to respectively encode the first meta-image, the second meta-image, and the third meta-image into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

[0020] A third aspect of the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0021] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which performs the steps of the above method when executed by a processor.

[0022] One or more of the above technical solutions have the following beneficial effects:

[0023] The present invention provides an optical encryption steganography method and system based on a multi-channel metasurface. Unlike most previous optical encryption work that uses the different responses of metasurfaces to different optical lighting conditions, the present invention, based on the ultra-high-resolution image display advantage of metasurfaces, introduces image-based steganography into the field of optical encryption, uses multiple images to disperse and carry secret information, and then encodes multiple images carrying secret information into optical images in the multi-channel metasurface for encrypted transmission.

[0024] In the present invention, by adjusting different key combinations such as wavelength and polarization for two nanostructures of different sizes on the multi-channel metasurface, a dual-structure non-spatial multiplexing three-channel metasurface is constructed, thereby achieving ultra-high-resolution encrypted display of three binary images at two wavelengths. This allows the multi-channel metasurface optical keys to have two levels, high and low, effectively reducing the risk of information being easily cracked due to a single key level.

[0025] In the present invention, multi-carrier information steganography is integrated into the field of metasurface optical encryption, giving full play to the advantages of metasurface in ultra-high-resolution image display and multi-channel joint regulation, and using full-channel encrypted optical images to jointly hide secret information, protecting the secret information from direct observation and leakage.

[0026] In the present invention, when extracting secret information, it is necessary to use optical keys to obtain the encrypted image information in all channels, and then combine the encrypted optical images in all channels to extract and decode the secret information, giving full play to the advantages of metasurfaces in multi-channel joint control.

[0027] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0029] Figure 1 This is a conceptual diagram of an optical encryption steganography method based on a multi-channel metasurface according to a first embodiment of the present invention;

[0030] Figure 2 Schematic diagram of the unit cell PT and PR structure of the supersurface nanostructure in Example 1 of the present invention;

[0031] Figure 3 Schematic diagram of simulated transmittance of polarized light incident along the L-axis and W-axis of the PT structure according to the first embodiment of the present invention;

[0032] Figure 4 Schematic diagram of simulated transmittance of polarized light incident along the L-axis and W-axis of the PR structure according to the first embodiment of the present invention;

[0033] Figure 5 Schematic diagram of simulated transmittance of the first channel and the second channel of the PT structure at different orientation angles at a wavelength of 633 nm according to the first embodiment of the present invention;

[0034] Figure 6 Schematic diagram of simulated transmittance of the first channel and the second channel of the PR structure at different orientation angles at a wavelength of 633 nm according to the first embodiment of the present invention;

[0035] Figure 7 Schematic diagram of theoretical transmittance corresponding to different structural orientation angles under the first channel and the second channel of Example 1 of the present invention;

[0036] Figure 8 Schematic diagram of the variation of total transmittance of the two structures with different orientation angles at a wavelength of 750 nm according to Example 1 of the present invention;

[0037] Figure 9 This is a schematic diagram of recording eight different binary codes into two different nanopillar structure orientation angles according to Example 1 of the present invention;

[0038] Figure 10 This is a schematic diagram of a process of run-length encoding a carrier image and preprocessing secret information according to an embodiment of the present invention;

[0039] Figure 11Schematic diagram of the process of embedding secret information into a carrier image in the first embodiment of the present invention;

[0040] Figure 12 The first meta-image retrieved using a higher-level optical key according to the first embodiment of the present invention;

[0041] Figure 13 The second meta-image retrieved using a higher-level optical key according to the first embodiment of the present invention;

[0042] Figure 14 The third meta-image retrieved using the optical key of a lower level according to the first embodiment of the present invention;

[0043] Figure 15 Schematic diagram of the process of extracting and recovering secret information according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0044] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0045] It should be noted that the terms used herein are for describing particular embodiments only and are not intended to limit the exemplary embodiments according to the present invention.

[0046] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0047] Example 1

[0048] This embodiment discloses an optical encryption steganography method based on a multi-channel metasurface. Figure 1 As shown, the following steps are included:

[0049] Step S1: construct a dual-structure non-spatial multiplexing three-channel metasurface based on the material properties of the dual-wavelength metasurface.

[0050] Step S1-1: constructing a dual-wavelength metasurface by forming hydrogenated amorphous silicon (a-Si:H) nanorods of two different sizes on a glass (SiO2) substrate.

[0051] In this embodiment, for convenience of representation, the two designed nanorods are named PT and PR. The first letter P indicates that the two nanobrick structures act as polarizers at wavelength λ1, and the second letters T and R represent the high transmittance and low transmittance of the structure at wavelength λ2, respectively. Among them, at wavelength λ2, the PT structure exhibits polarization-independent efficient transmission, and the PR structure exhibits polarization-independent efficient reflection (corresponding to low transmittance). "Polarization-independent" means that regardless of the polarization of the incident light, one structure can efficiently transmit the incident light, while the other structure can efficiently reflect the incident light.

[0052] like Figure 2 As shown in the figure, two rectangular unit cell structures with PT and PR functions are shown. Their geometric parameters are: PT length is L1 = 60nm, width is W1 = 130nm, and height is H1 = 220nm; PR length is L2 = 140nm, width is W2 = 225nm, and height is H2 = 220nm. The period of the unit cell is P = 320nm.

[0053] like Figure 3 and Figure 4 Figure 2 shows the transmission spectra of the PT and PR structures for linearly polarized light incident along the L and W axes, respectively. The results show that at wavelength λ1, the transmittance differences between the polarized and unpolarized axes for the PT and PR structures are approximately 87% and 75%, respectively. At wavelength λ2, the transmittance of the PT structure is above 94% along both axes, while the transmittance of the PR structure is below 2%, meeting the requirements. Furthermore, both structures maintain their expected characteristics near the designed operating wavelength, demonstrating the robustness of the structural functionality to wavelength variations.

[0054] Step S1-2: selecting an operating wavelength λ1 and an operating wavelength λ2 based on the material properties of the dual-wavelength metasurface.

[0055] In this embodiment, considering the high refractive index and low absorption of a-Si:H material in the near-infrared band, two operating wavelengths of λ1 = 633 nm and λ2 = 750 nm are selected.

[0056] Step S1-3, at an operating wavelength λ1, using the two nanorods of different sizes as nanopolarizers, placing a polarizer and an analyzer in front and behind them, respectively, and constructing two non-orthogonal polarization light paths by regulating the orientation angles of the nanorods and the directions of the polarizer and analyzer, which are defined as a first channel and a second channel, respectively;

[0057] The intensity of the output light can be controlled by fixing the orientation angle α of the structure. By setting different combinations of the polarization direction θ1 and the analysis direction θ2, two non-orthogonal polarization light paths are constructed, thereby realizing a dual-channel design in which the transmitted light intensity at wavelength λ1 depends on the structural orientation angle.

[0058] When the nanostructure is used as a nanopolarizer, the intensity of the output light can be controlled by fixing the orientation angle of the structure, specifically:

[0059] It is known that the Jones matrix M of a nanorod with an orientation angle α in a plane is α It can be expressed as:

[0060]

[0061] Where R(α) is the rotation matrix, M0 represents the Jones matrix of an ideal nanorod that does not produce cross-polarization components, and A and B are the complex transmission (or reflection) coefficients of light polarized along the x-axis and y-axis, respectively.

[0062] Because the Jones matrix has a close connection between the input and output fields, this embodiment uses a polarizer and analyzer to control the polarization direction of the incident and transmitted light. Therefore, when linearly polarized light with a polarization angle of θ1 (Jones vector J0) is incident, the transmitted light passes through the analyzer, and the Jones vector J1 of the final output light can be expressed as:

[0063]

[0064] Where θ1 and θ2 are the transmission axis directions of the polarizer and analyzer respectively. is the Jones matrix of the polarizer. When the intensity of the incident linear polarized light is I0, after passing through the polarizer, the calculation formula of the outgoing light intensity is:

[0065]

[0066] When the nanostructure is regarded as an ideal polarizer (let A = 1, B = 0), the formula for the output light intensity can be simplified to:

[0067]

[0068] Based on the above equation, by carefully selecting different combinations of the polarizer's polarization direction θ1 and the analyzer's transmission direction θ2, a dual-channel design in which the transmitted light intensity depends on the structural orientation angle can be achieved. As a verification example, the polarizer and analyzer combinations selected here are: first channel: θ1 = 30° and θ2 = 75°; second channel: θ1 = -15° and θ2 = 30°.

[0069] In this embodiment, based on Malus's law, the transmittance of the PT and PR structures under dual channels is simulated and studied at wavelength λ1. The results are as follows: Figure 5 and Figure 6 As shown in the figure, the curve shows the trend of structural transmittance changing with different orientation angles.

[0070] In order to intuitively compare the difference between the two structures as nanopolarizers and theoretical polarizers in dual-channel design, Figure 7 The theoretical transmittance of the dual-channel structure at different orientation angles is shown. In the figure, the gray dashed lines mark the four selected orientation directions and their corresponding two-bit binary intensity coding states in the dual-channel structure.

[0071] like Figure 7 As shown, the codes 00-11 are determined according to the light intensity. Figure 7 The distribution curves of the transmitted light intensity under these two channels as a function of the structural orientation angle are shown. It can be seen that the simulation curves of the two selected structures are consistent with the change trends of the theoretical curves.

[0072] We selected four fixed structural orientation angles for each nanopillar: 30°, 75°, 120°, and 165°. We encoded the light intensity of the two channels at these four orientation angles, with high intensity encoded as 1 and low intensity as 0. We also recorded four different binary encoding states for the two channels at these wavelengths: "11," "10," "00," and "01." This enabled us to encode two binary images in the polarizer channel. Experiments showed that at these four selected angles, the dual-channel transmittance of the two structures exceeded 72% of the theoretical transmittance.

[0073] Step S1-4: constructing a third channel at the operating wavelength λ2 according to the different transmitted light intensities of the two nanorods of different sizes.

[0074] Since the transmitted light intensity of the two structures is only related to the wavelength and is independent of the incident polarization state and the structural orientation angle, an additional single independent channel can be designed at this wavelength.

[0075] In this embodiment, by encoding the PT structure as 1 and the PR structure as 0, an image encoding channel completely independent of the first two channels is designed at wavelength λ2.

[0076] At wavelength λ2, the PT structure has high light intensity at the four selected orientation angles (30°, 75°, 120°, and 165°), and thus is encoded as 1 at these four angles. Meanwhile, the PR structure has low light intensity, and thus is encoded as 0 at these four angles. Therefore, at wavelength λ2, the PT structure is encoded as 1, and the PR structure is encoded as 0.

[0077] like Figure 8Figure 2 shows the total transmittance distribution of the PT and PR structures at different orientation angles at wavelength λ2. It can be seen that as the orientation angle changes, the total transmittance of the PT structure remains stable near 1, while the total transmittance of the PR structure remains stable around 0. This demonstrates that at operating wavelength λ1, the encoding of channels 1 and 2 is dependent on the orientation angle of the structures, independent of their size. At operating wavelength λ2, the total transmittance of these two structures is independent of the incident polarization state and the orientation angle of the structures, but is dependent on their size.

[0078] Since the metasurface in the present invention is a multi-channel metasurface based on a dual structure, the selection of the polarizer structure for the first channel and the second channel will determine the specific size of the nanopillars (PT or PR) to be used according to the encoding in the third channel. Figure 9 The corresponding relationship between the nanopillar structure array and the light intensity coding distribution of the three channels is shown. It can be seen that each nanopillar participates in the information recording of three images. The three binary images after optical encryption are composed of 8 binary codes from 000 to 111. The first two bits of the three-bit code (channel 1 and channel 2) are distinguished by the structural orientation angle, and the third bit (channel 3) is distinguished by the structural size (PT or PR).

[0079] Based on the structure and design principles selected above, it is possible to encode three images into a single-layer metasurface, providing an optical encryption barrier for the meta-image that transmits secret information extraction and recovery parameters and the meta-image that embeds secret information.

[0080] By adjusting different key combinations such as wavelength and polarization through two nanostructures of different sizes, different optical key levels can be constructed. This is very different from the previous design of three-channel metasurface encryption display with joint regulation of wavelength and polarization state, and lays the foundation for the design of high and low-level optical keys.

[0081] Step S2: obtaining secret information, performing scrambling preprocessing to obtain scrambled secret information, generating a QR code using parameters extracted and recovered from the secret information, and obtaining a first meta-image;

[0082] In this embodiment, a 14×14 pixel binary image is the final hidden secret information, and the content displayed is META.

[0083] Since the secret information has continuous identical pixels, in order to avoid regularity and further increase the security of the information, such as Figure 10 As shown, a logistic map is used to generate an iterative sequence with non-periodic and non-convergent properties to scramble the secret information and obtain the scrambled secret information.

[0084] The expression of scrambling preprocessing is:

[0085]

[0086] Among them, x n is the state value of the nth iteration , x n+1 is x n The next state value, μ is the control parameter (μ Since the domain of the resulting iterative sequence is between [0, 1], in order to perform an XOR operation with the secret information, the threshold is defined as the initial value x0 of the logistic map to construct a 14×14 binary matrix.

[0087] The initial value x0 of the logistic map is used as a string "0.4214" that transmits the secret information extraction and recovery parameters to generate a QR code and obtain the first meta-image;

[0088] Among them, 4 represents the value of μ in the mapping formula; 2 represents the hint information of the embedding position; 14 represents the pixel size of the secret information; and the overall value of 0.4214 represents the initial value x0 of the logistic mapping, which has a domain between 0 and 1 and is used to convey parameter information about the extraction and recovery of secret information.

[0089] Step S3: Based on the run-length coding steganography algorithm, two carrier images are selected. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequences of the two carrier images, and the images are reconstructed to obtain the second and third meta-images embedded with the secret information.

[0090] Run-length encoding (RLE) is considered a popular compression technique. In RLE, when characters in a string appear consecutively, they are replaced by the number of times they appear, which is called the run-length value.

[0091] In this embodiment, the carrier image is a binary image. Since binary images contain many consecutive identical black and white pixels, they can also be run-length encoded. The specific steps are as follows:

[0092] Step S3-1: Select two binary carrier images of 50×50 pixels.

[0093] like Figure 13 、 14 As shown, carrier image 1 is a cartoon animal, and carrier image 2 is a cartoon girl, and their pixels are run-length encoded respectively.

[0094] Step S3-2: The carrier image 1 can be regarded as a 50×50 matrix, in which white pixels are represented as 1 and black pixels are represented as 0, so it can be scanned column by column to convert its dimensions into a continuous 01 sequence.

[0095] Step S3-3: Run-length encoding is performed on the obtained continuous 01 sequence, and continuous black and white pixels are replaced by the number of times they appear; after encoding, all the run-length values ​​constitute a run sequence and are named L1, and its length is defined as Length(L1).

[0096] In this embodiment, based on the carrier image 1 we selected, the first run length value of the sequence is 215, which is represented by 215 consecutive 1s, that is, 215 consecutive white pixels.

[0097] Step S3-4: Similarly, the sequence formed by the run-length encoding of the carrier image 2 is named L2, and its length is Length(L2).

[0098] Since the carrier image is a binary image, any information to be hidden needs to be converted into a binary sequence if it is to be embedded in it.

[0099] Step S3-5: Scan the scrambled secret information obtained in step S2 column by column to obtain a 01 sequence (Pixel) to be embedded.

[0100] Step S3-6: embed the information in the 01 sequence to be embedded into the run sequence L1 and L2 in a dispersed manner according to the bit, to obtain the run sequence after the information is embedded.

[0101] like Figure 11 As shown, during embedding, the run length values ​​(black pixel runs) corresponding to the same even-numbered positions in L1 and L2 are first checked. When the embedded information bit is 0, the larger value is modified (by 1) to make them have the same parity. When the information bit is 1, the larger value is similarly modified to make them have different parities (if the two run length values ​​are the same, sequence L1 is modified by default). If the position embedded in the run sequence exceeds the length of L1, this remaining information is embedded only in L2. At this time, if the information bit is 0, the run length value at the corresponding position in L2 is modified (by 1) to an even number; otherwise, it is modified to an odd number. Otherwise, if the parity and the value to be embedded meet the rules, no modification is made.

[0102] In this embodiment, when a run length value is modified, the last bit of the same consecutive binary number in the uncoded state is modified, that is, it changes from 0 to 1, and the corresponding pixel of the carrier image changes from black to white. According to the above rules, the secret information is hidden in two run sequences. The run sequences after embedding the information are named L and L respectively. # 1 and L # 2.

[0103] Step S3-7, the game program sequence L after the embedded information # 1 and L# 2 respectively perform the inverse process of run-length encoding, recover the continuous black and white pixels by decoding the run-length values ​​in the sequence, and then reconstruct the two images embedded with secret information to obtain the second super-image and the third super-image.

[0104] Step S4: Encode the first meta-image, the second meta-image, and the third meta-image into the dual-structure non-spatial multiplexing three-channel metasurface respectively to realize optical encryption.

[0105] In this embodiment, the three images of the QR code, the reconstructed cartoon animal, and the reconstructed cartoon girl are named as the first meta-image, the second meta-image, and the third meta-image, respectively.

[0106] Since all three images are binary images, that is, black and white pixel images (black pixels are 0 and white pixels are 1), we have previously implemented three-channel encoding at two wavelengths, that is, 000-111. Here, we define the first bit of the three-bit encoding to represent the first channel, the second bit to represent the second channel, and the third bit to represent the third channel. Now we need to encode these three binary images into three channels on a pixel-by-pixel basis.

[0107] For example, at the same pixel position of the three images in the three channels, the pixels are all black pixels (ie 0), then the code of the three channels at this pixel position is 000, so you need to select the structural rotation angle (120°) of 00 code (channel 1 and channel 2), and the structural type (PR) of 0 (channel 3); if the three images in the three channels are encoded as 101 at the same pixel position (ie white and black: channel 1 is white, channel 2 is black, and channel 3 is white), you need to select the structural rotation angle (75°) of 10 code (channel 1 and channel 2), and the structural type (PT) of 1 (channel 3); and the same applies to other codes.

[0108] In this embodiment, in order to verify the feasibility of the proposed optical encryption steganography method based on multi-channel metasurface, we constructed a corresponding single-layer metasurface structure array by carefully selecting specific nanopillars and setting their orientation angles.

[0109] Specifically, three images of the same size (50 × 50 pixels) were recorded simultaneously to 64 × 64 μm 2 In the metasurface sample, each pixel corresponds to a 4×4 array of nanopillars. Using the metasurface, the decryptor can obtain the final transmitted information through a two-step operation.

[0110] The specific process of step S5, decryption is as follows:

[0111] 1. The decryptor needs to use different optical keys to extract the high-resolution images encrypted in all channels, which is the basis for accurate information extraction. Considering the case of a higher key level, at a wavelength of λ1 = 633nm, in order to observe the hidden images in two different channels, it is necessary to insert an optical polarizer and analyzer before and after the metasurface to control the polarization direction of the incident light and the transmitted light respectively, and generate two images under two non-orthogonal polarization paths (i.e., the first meta-image: θ1 = 30° and θ2 = 75°, the second meta-image: θ1 = -15° and θ2 = 30°), as shown in Figure 2. Figure 12 and Figure 13 Considering the case of a lower key level, at a wavelength of λ2 = 750nm, the encrypted third meta-image can be observed under any polarization state of light incident, as shown in Figure 14 As shown, by incident light of arbitrary polarization, the third meta-image can be directly obtained from the outgoing light intensity distribution.

[0112] 2. If Figure 15 As shown, the algorithm combines full-channel optical images for information extraction and recovery. The decryptor first obtains the information extraction and recovery parameter 0.4214 by scanning the first meta-image, which is crucial for ultimately accurately obtaining the secret information.

[0113] The specific process of secret information extraction and recovery is as follows:

[0114] The decryptor needs to perform binarization and run-length encoding on the second and third super-structured images respectively, so as to obtain the run-length sequence L of the two images. # 1 and L # 2. Then, the parity of the run length values ​​corresponding to the same even position in the two run sequences is compared simultaneously. If the parity is the same, the information binary bit extracted at that position is 0, otherwise it is 1. When the extracted position exceeds the sequence L # 1, the information will only be in sequence L # 2. When L # When the run length value of the extraction position in 2 is an even number, the information bit extracted at this position is 0, otherwise it is 1.

[0115] After extracting all the information, the hidden scrambled secret information is reconstructed and subjected to an XOR logic operation with the iterative sequence generated by the parameter string 0.4214 to recover the hidden secret information.

[0116] It is worth mentioning that the three meta-images encrypted in the metasurface play an equally important role in the final extraction and recovery of secret information. Although the acquisition of secret information only requires two steps, if any of the images is not correctly obtained during the metasurface optical decryption link, or if the information encryption and decryption process is unclear, the secret information will ultimately not be accurately extracted.

[0117] Most previous optical encryption works based on metasurfaces have used the different responses of metasurfaces to different optical lighting conditions (optical keys) to directly encrypt secret information by imaging, ignoring the metasurface's ultra-high-resolution image display and its advantages in multi-channel joint control.

[0118] Based on the ultra-high-resolution image display advantages of metasurfaces, this invention introduces image-based steganography into the field of optical encryption. Multiple images are used to disperse secret information, and then these images carrying secret information are encoded into optical images within a multi-channel metasurface for encrypted transmission. The designed multi-channel metasurface with wavelength and polarization multiplexing also assigns different levels of optical keys to the carrier images embedded with secret information, further enhancing the security of the secret information. Furthermore, to extract the secret information, the optical keys are used to obtain the encrypted image information in all channels. This is then combined with the encrypted optical images in all channels to extract and decode the secret information, fully leveraging the metasurface's advantages in multi-channel joint regulation.

[0119] Example 2

[0120] The purpose of this embodiment is to provide an optical encryption steganography system based on a multi-channel metasurface, comprising:

[0121] The channel construction module is configured to: construct a dual-structure non-spatial multiplexing three-channel metasurface based on the material properties of the dual-wavelength metasurface;

[0122] The meta-image acquisition module is configured to: acquire secret information, perform scrambling preprocessing to obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first meta-image;

[0123] A steganographic algorithm based on run-length coding selects two carrier images. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images. The images are then reconstructed to obtain the second and third super-images embedded with the secret information.

[0124] The optical encryption module is configured to respectively encode the first meta-image, the second meta-image, and the third meta-image into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

[0125] Example 3

[0126] The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0127] Example 4

[0128] The purpose of this embodiment is to provide a computer-readable storage medium.

[0129] A computer-readable storage medium stores a computer program, which, when executed by a processor, performs the steps of the above method.

[0130] The steps involved in the apparatus of the above embodiment correspond to those of the method embodiment 1. For detailed implementation, please refer to the relevant description of embodiment 1. The term "computer-readable storage medium" should be understood to mean a single medium or multiple media containing one or more instruction sets; it should also be understood to include any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and causing the processor to perform any method of the present invention.

[0131] Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using a general-purpose computer device. Alternatively, they can be implemented using program code executable by a computing device, which can then be stored in a storage device and executed by the computing device. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0132] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. An optical encryption steganography method based on a multi-channel metasurface, characterized in that: include: Based on the material properties of the dual-wavelength metasurface, a dual-structure non-spatial multiplexing three-channel metasurface was constructed. The specific steps are as follows: a dual-wavelength metasurface is constructed by hydrogenated amorphous silicon nanorods of two different sizes on a glass substrate; Based on the material properties of the dual-wavelength metasurface, a working wavelength λ1 and a working wavelength λ2 are selected; At an operating wavelength of λ1, the two nanorods of different sizes are used as nanopolarizers, and a polarizer and an analyzer are placed in front and behind them, respectively. By regulating the orientation angle of the nanorods and the directions of the polarizer and analyzer, two non-orthogonal polarization light paths are constructed, which are defined as the first channel and the second channel respectively. At the operating wavelength λ2, constructing a third channel according to the different transmitted light intensities of the two nanorods of different sizes; Obtain secret information, perform scrambling preprocessing to obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first meta-image; A steganographic algorithm based on run-length coding selects two carrier images. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images. The images are then reconstructed to obtain the second and third super-images embedded with the secret information. The first meta-image, the second meta-image and the third meta-image are respectively encoded into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

2. The optical encryption steganography method based on a multi-channel metasurface according to claim 1, characterized in that: The specific steps of obtaining the second meta-image and the third meta-image embedded with secret information are: selecting two carrier images, defined as a first carrier image and a second carrier image; For the first carrier image, represent its white pixels as 1 and its black pixels as 0, scan it column by column, and convert its dimensions into a continuous sequence of 0 and 1; Run-length encoding is performed on the obtained continuous 01 sequence, and continuous black and white pixels are replaced by the number of times they appear; all the run-length values ​​after encoding constitute a run sequence and are named L1; The run-length sequence formed by run-length encoding the second carrier image is named L2; Performing scrambling preprocessing on the embedded secret information to obtain scrambled secret information; Scanning the scrambled secret information column by column to obtain a 01 sequence to be embedded; The information in the 01 sequence to be embedded is scattered and embedded into the game sequences L1 and L2 bit by bit to obtain the game sequence after the information is embedded; The game sequence after embedding the information is represented as L # 1 and L # 2.

3. The optical encryption steganography method based on a multi-channel metasurface according to claim 2, characterized in that: The image reconstruction is specifically to reconstruct the game sequence L after the embedded information # 1 and L # 2 respectively perform the inverse process of run-length encoding, recover the continuous black and white pixels by decoding the run-length values ​​in the run sequence, and then reconstruct the second meta-image and the third meta-image after embedding the secret information.

4. The optical encryption steganography method based on a multi-channel metasurface according to claim 1, characterized in that: The scrambling preprocessing is specifically to use logistic mapping to generate an iterative sequence with non-periodic and non-convergent properties to perform scrambling preprocessing on the secret information.

5. The optical encryption steganography method based on a multi-channel metasurface according to claim 2, characterized in that: The information in the 01 sequence to be embedded is embedded bit by bit into the game sequence L1 and L2 to obtain the game sequence after the information is embedded, specifically: When embedding, first detect the run length values ​​corresponding to the same even positions in L1 and L2. When the embedded information bit is 0, modify the larger value of the two to make them have the same parity; when the information bit is 1, also modify the larger value of the two to make them have different parities; when the position embedded in the run sequence exceeds the length of L1, the remaining information will only be embedded in L2. At this time, when the information bit is 0, the run length value of the corresponding position in L2 is modified to an even number; otherwise, it is modified to an odd number; when the parity and the value to be embedded meet the rules, no modification is made.

6. The optical encryption steganography method based on a multi-channel metasurface according to claim 1, characterized in that: Decrypting the encrypted first meta-image, second meta-image, and third meta-image includes: obtaining the working wavelength used during encryption, obtaining the first meta-image and the second meta-image by adjusting the directions of a polarizer and an analyzer at the working wavelength λ1, and directly obtaining the third meta-image from the intensity distribution of the output light by incident light of arbitrary polarization at the working wavelength λ2; Scanning the first meta-image to obtain parameters for extracting and recovering the secret information; The acquired second meta-image and third meta-image are binarized and run-length encoded respectively to obtain the run-length sequence L of the second meta-image and the third meta-image. # 1 and L # 2; Compare the program sequence L # 1 and L # 2, the parity of each run length value corresponding to the same even position is calculated and information is extracted; After extracting all the information, the hidden scrambled secret information is reconstructed and subjected to an XOR logic operation with the iterative sequence generated by the parameter string to recover the steganographic secret information.

7. An optical encryption steganography system based on a multi-channel metasurface, characterized in that: include: The channel construction module is configured to: construct a dual-structure non-spatial multiplexing three-channel metasurface based on the material properties of the dual-wavelength metasurface; the specific steps are as follows: constructing the dual-wavelength metasurface by hydrogenated amorphous silicon nanorods of two different sizes on a glass substrate; Based on the material properties of the dual-wavelength metasurface, a working wavelength λ1 and a working wavelength λ2 are selected; At an operating wavelength of λ1, the two nanorods of different sizes are used as nanopolarizers, and a polarizer and an analyzer are placed in front and behind them, respectively. By regulating the orientation angle of the nanorods and the directions of the polarizer and analyzer, two non-orthogonal polarization light paths are constructed, which are defined as the first channel and the second channel respectively. At the operating wavelength λ2, constructing a third channel according to the different transmitted light intensities of the two nanorods of different sizes; The meta-image acquisition module is configured to: acquire secret information, perform scrambling preprocessing to obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first meta-image; A steganographic algorithm based on run-length coding selects two carrier images. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images. The images are then reconstructed to obtain the second and third super-images embedded with the secret information. The optical encryption module is configured to respectively encode the first meta-image, the second meta-image, and the third meta-image into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method described in any one of claims 1 to 6 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method described in any one of claims 1 to 6 are performed.

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